In general, in a DVD disk on the market, in which a movie, music or the like is collected (recorded), data information such as images, voices or the like is ciphered and recorded in order to protect its copyright against an illegal use thereof. Thus, when the DVD disk is played back using a DVD player, the DVD player plays back it by reading key information recorded in a subaltern information region of the same DVD disk, and deciphering the ciphered data information using the key information to reconstruct the original images, voices or the like.
Hereinafter, a conventional DVD disk and a disk player of the above-mentioned type will be described. FIG. 12 is a perspective view showing a rough construction of the above-mentioned conventional DVD disk. In FIG. 12, 101 denotes the DVD disk. 102 denotes a main information region of the DVD disk 101. Data information such as images, voices or the like is generally ciphered and recorded in the main information region 102. 103 denotes a key information region which records key information for deciphering the data information recorded in the main information region 102. The key information region 103 is located at an inner periphery side in the DVD disk 101.
FIG. 11 is a block diagram showing a rough construction of the conventional DVD player. In FIG. 11, 101 denotes the DVD disk shown in FIG. 12, which also records the data information such as images or voices to be played back. 104 denotes an optical pickup which reads record signals of the DVD disk 101 using a laser ray. 105 denotes a transfer controller which moves the optical pickup 104 in the radial direction of the DVD disk 101 in order to read the record signals at arbitrary positions on the DVD disk 101. 106 denotes a disk motor which rotates the DVD disk 101. 107 denotes a first control circuit control circuit 109 digitizes (makes binary) the input which controls the optical pickup 104, the transfer controller 105 and the disk motor 106. 108 denotes an amplifier which amplifies the signals which have been read by the optical pickup 104. 109 denotes a second control circuit into which the output signals of the amplifier 108 are inputted. Based on the signals, the second control circuit 109 generates servo signals, such as focus error signals or tracking error signals, which are required when the optical pickup 104 reads the DVD disk 101, and then outputs them to the first control circuit 107. Further, the second signals of analog type. 110 denotes a demodulation circuit which analyzes the signals which have been read from the DVD disk 101 and digitized, and reconstructs the data information such as the original images or music. 111 denotes a system control circuit which controls the whole DVD player.
Hereinafter, actions of the DVD player having the above-mentioned construction will be described. When the DVD disk on the market is played back, at first, the transfer controller 105 is driven by the first control circuit 107 in accordance with the instruction of the system control circuit 111 so as to move the optical pickup 104 to an inner periphery side in the DVD disk 101. The signals, which have been read by the optical pickup 104, are amplified by the amplifier 108, and further digitized by the second control circuit 109. Then, the contents of the signals are read by the demodulation circuit 110. The modulation circuit 110 sends the results to the system control circuit 111. Then, the system control circuit 111 outputs another instruction to the first control circuit 107 again, if the read contents do not include the key information of the key information recording region 103 (see FIG. 12). Thus, the transfer controller 105 is driven by the first control circuit 107 so as to move the optical pickup 104 to a more inner position of the DVD disk 101, and then the key information is searched.
The key information recorded in the inner portion of the DVD disk 101 is found by repeating the abovementioned actions so that the information is read by the demodulation circuit 110. If the system control circuit 111 detects that the modulation circuit 110 has read the key information of the DVD disk 101, the transfer controller 105 is driven by the first control circuit 107 in accordance with the instruction of the system control circuit 111 so as to move the optical pickup 104 to an outer periphery side. Then, the optical pickup 104 reads the record signals in the main information region 102 of the DVD disk 101 (see FIG. 12). Because the record signals are generally ciphered, normal image signals or voice signals cannot be obtained if the record signals are played back as they stand. However, the record signals can be deciphered if the key information, which is recorded in the key information recording region 103 and has been read, is used. Thus, the demodulation circuit 110 deciphers the record signals of the main information region 102 using the key information which has been read so as to reconstruct the original and normal image data or voice data.
However, in the writable optical disk such as a DVD-R or the like, a copy of the optical disk may be easily produced by copying the subaltern information region, too. As a physical means for preventing it, there has been proposed such a method to form other information previously by means of pre-pits in the key information region.
The above-mentioned pre-pits will be described with reference to FIG. 9. FIG. 9 shows a section which is made by cutting a DVD disk 1 on the market along its radial direction, and the recording condition of the information therein. In FIG. 9, the left side is the inner periphery side of the disk, while the right side is the outer periphery side of the disk. Hereupon, 32 denotes a main information region (main recording region), while 33 denotes a key information recording region. Further, 43 denotes first key information, which is recorded in the key information recording region 33. 44 denotes a main data, which is recorded in the main information region 32. Although the main data 44 such as an image data or a music data is ciphered, it can be deciphered by using the first key information 43.
45 denotes a writable DVD disk (DVD-R disk). In the main information region 32 of the disk, signals can be freely recorded. 46 denotes other key information (second key information) which has been previously formed by means of pre-pits instead of the normal key information. The other key information has been previously recorded in the key information recording region 33 of the writable DVD disk 45 in such a manner that it cannot be rewritten. The second key information 46 is a data which is not available for the use of deciphering the cipher. That is, the second key information cannot decipher the cipher of any of the main data 44. Meanwhile, the contents in the main data 44 recorded in the main information region 32 of the writable DVD disk 45 are quite as same as those in the main data 44 of the original DVD disk 1.
However, even if someone intends to play back the writable DVD disk 45 using the above-mentioned DVD player, the second key information 46 recorded in the key information recording region 33 disposed at a predetermined position in the inner periphery portion of the writable DVD disk is the unavailable data which is different from the original data for deciphering the cipher, as described above. Therefore, even if the unavailable key information is used, the ciphered data cannot be reconstructed to the original and normal image signals or voice signals. As a consequence, it is designed that the illegally copied writable DVD disk cannot be played back.
Although the illegal copy can be prevented in the ordinary apparatus as described above, it is probable that the key information as well as the data information is also copied into the main information region by using a remodeled drive or the like. Hereinafter, there will be described such a case that not only the main data but also the key information is copied and recorded in the main information region of the writable DVD disk.
FIG. 10 is a view showing a read only DVD disk on the market, which is the original of copying and has normal key information only. Hereupon, FIG. 10 shows such a state that the key information and the contents of the writable DVD disk on the market, in which a movie, music or the like is collected, are copied to the main information region.
As shown in FIG. 10, both of the main data 44 and the first key information 43 of the original DVD disk 1 are copied and recorded in the main information region 32 of the writable DVD disk 45. Although the second key information 46, which is the original key information, has been previously recorded in the key information recording region 33 of the writable DVD disk 45, the second key information 46 is the unavailable data for deciphering the data of the main information region 32, as described above. In this case, it is impossible to decipher the main data 44 using the second key information 46 located at the predetermined position. However, it is possible to decipher the cipher, if the first key information. 43 recorded in the main information region 32, which is not located at the predetermined position, is used.
Hereinafter, there will be described such a case that a writable DVD disk is played back using a DVD player with reference to FIG. 3 for the later-mentioned Embodiment 3 or 4 of the present invention for convenience's sake. In FIG. 3, at first, a transfer controller 4 is driven by first control means 6 in accordance with second control means 9 so as to move an optical pickup 3 to the second subaltern information region located at the most inner periphery side of a DVD disk 1. The optical pickup 3 reads disk information signals such as the disk type information and positional information of the first subaltern information region, which are stored in the second subaltern information region. The signals are amplified by an amplifier 5. Further, the contents of the signals are detected by demodulation means 7, and then judged by disk judging means 14. In accordance with the read positional information of the first subaltern information region, the second control means and the first control means 6 drive the transfer controller 4 and make the transfer controller 4 move the optical pickup 3. Thus, the disk control information, which includes the key data of the first subaltern information region located at the normal position, is read.
However, in the conventional playback system or copy system for the DVD disk, if each of the ciphered data information such as a movie or music and the key information for deciphering the data information in the DVD disk on the market is copied to the DVD-R or RW disk, each of which is a user-writable DVD disk, it is probable that the ciphered data information may be deciphered to be played back on the basis of the key information which has been copied to the writable DVD disk. In consequence, in the conventional system, there exists such a problem that illegal uses of the DVD disk or other optical disks, which infringe the copyrights, cannot be effectively prevented.